User blog comment:Parinwaris/The Center Of Theories.../@comment-30134594-20171019130435/@comment-31658174-20171020223356

My theory:

After getting past the champ, you get an item from him/her. He/She tells you to go to Aredia Ccatacombs and use it behind the pedestals for the keys of time and space. You then have to solve 6 puzzles (3 for each key) to get them. Once you use both of them and put them on the pedestals, Giratina appears. After catching Giratina, you have to add it to your party (by having an extra space OR swapping a team member) and then Giratina will open two portals, leading you to Dialga and Palkia.